U.S. patent application number 10/645038 was filed with the patent office on 2005-02-24 for apparatus for functional and stress testing of exposed chip land grid array devices.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Cannon, Lonnie J., Corbin, John Saunders JR., Gardell, David Lewis, Garza, Jose Arturo, Kutner, Jeffrey Frank, Larsen, Kenneth Carl, Mahaney, Howard Victor JR., Salazar, John Joseph.
Application Number | 20050040838 10/645038 |
Document ID | / |
Family ID | 34194219 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050040838 |
Kind Code |
A1 |
Cannon, Lonnie J. ; et
al. |
February 24, 2005 |
Apparatus for functional and stress testing of exposed chip land
grid array devices
Abstract
A chip testing system with improved thermal performance. In a
preferred embodiment, a nest assembly of a chip testing apparatus
includes tooling balls and a fitted frame for improving alignment
of a coldplate and a chip surface. In preferred embodiments, the
coldplate is of unibody design. Thermal performance is also
improved by balancing the forces exerted on the coldplate using an
adjustable hose mounting bracket. The bracket allows the forces
exerted by the hoses on the coldplate to be adjusted so they
balance and cancel other unwanted forces on the cold plate.
Inventors: |
Cannon, Lonnie J.; (Austin,
TX) ; Corbin, John Saunders JR.; (Austin, TX)
; Gardell, David Lewis; (Fairfax, VT) ; Garza,
Jose Arturo; (Pflugerville, TX) ; Kutner, Jeffrey
Frank; (Pleasant Valley, NY) ; Larsen, Kenneth
Carl; (Georgetown, TX) ; Mahaney, Howard Victor
JR.; (Cedar Park, TX) ; Salazar, John Joseph;
(Austin, TX) |
Correspondence
Address: |
IBM CORP (YA)
C/O YEE & ASSOCIATES PC
P.O. BOX 802333
DALLAS
TX
75380
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
34194219 |
Appl. No.: |
10/645038 |
Filed: |
August 21, 2003 |
Current U.S.
Class: |
324/750.08 |
Current CPC
Class: |
G01R 31/2891
20130101 |
Class at
Publication: |
324/765 |
International
Class: |
G01R 031/26 |
Claims
What is claimed is:
1. An integrated circuit testing apparatus that provides thermal
control of a device under test, comprising: a coldplate, the
coldplate including tooling balls formed on the coldplate; a load
frame positioned beneath the coldplate, the load frame including
locator features; wherein the locator features engage the tooling
balls such that rotation of the coldplate is restricted about a
first axis of rotation, but is permitted about second and third
axes of rotation, and such that transverse motion of the coldplate
with respect to the load frame is restricted.
2. The apparatus of claim 1, wherein the tooling balls are
cylindrical with semi-spherical ends.
3. The apparatus of claim 1, wherein the tooling balls are formed
on load flanges of the coldplate.
4. The apparatus of claim 1, wherein the coldplate includes
features for mounting, aligning, and suspending the coldplate, and
features for accommodating cartridge heaters, thermocouples, and
gas flow; and wherein the coldplate and features are of unibody
design.
5. The apparatus of claim 1, further comprising side frames for
supporting a nest structure that includes the coldplate, wherein
the sideframes are pinned to a clamp plate such that the side
frames can be separated from the clamp plate and reassembled while
maintaining positional tolerances.
6. The apparatus of claim 1, further comprising a pogo pin socket
having probe pins and supported by corner pins, the corner pins
supported by springs; wherein a load placed on the socket
compresses the corner pins and the probe pins of the socket.
7. An integrated circuit testing apparatus that provides thermal
control of a device under test, comprising: a nest assembly that
includes a coldplate, the coldplate being supplied with chilled
fluid by fluid lines for cooling the device under test; wherein
first ends of the fluid lines connect to supply chilled fluid to
and remove chilled fluid from the coldplate, and wherein second
ends of the fluid lines connect to an adjustable clamp; and wherein
the fluid lines exert a force on the coldplate, and wherein the
force exerted by the fluid lines cancels other forces exerted on
the cold plate such that a net force between the coldplate and the
device under test is substantially resolved at a vector center of
the device under test.
8. The apparatus of claim 7, wherein the coldplate includes
features for mounting, aligning, and suspending the coldplate, and
features for accommodating cartridge heaters, thermocouples, and
gas flow; and wherein the coldplate and features are of unibody
design.
9. The apparatus of claim 7, further comprising side frames for
supporting a nest structure that includes the coldplate, wherein
the sideframes are pinned to a clamp plate such that the side
frames can be separated from the clamp plate and reassembled while
maintaining positional tolerances.
10. The apparatus of claim 7, further comprising a pogo pin socket
having probe pins and supported by corner pins, the corner pins
supported by springs; wherein a load placed on the socket
compresses the corner pins and the probe pins of the socket.
11. The apparatus of claim 7, wherein the adjustable clamp attaches
to a bracket on a card cage bulkhead.
12. The apparatus of claim 7, wherein the coldplate includes
tooling balls formed thereon, and wherein the tooling balls fit
into alignment structures of a load frame to restrict movement of
the coldplate about an axis substantially perpendicular to the
plane of the coldplate and such that transverse motion of the
coldplate with respect to the load frame is restricted.
13. A method of testing an integrated circuit, comprising the steps
of: supplying a coldplate of a testing apparatus with chilled
fluid, wherein the coldplate includes structures protruding from
the coldplate; positioning the coldplate adjacent to a load frame,
the load frame having receptacles positioned to engage the
structures protruding from the coldplate; aligning the coldplate
with a device under test; wherein when the coldplate is positioned
adjacent to the load frame, the structures engage the receptacles
such that the coldplate is free to rotate about an axis
perpendicular to the coldplate, but allowed to rotate about two
axes parallel with the coldplate, and such that transverse motion
of the coldplate with respect to the load frame is restricted.
14. The method of claim 13, wherein the structures are
semispherical tooling balls fitted into load flanges of the
coldplate.
15. The method of claim 13, wherein the structures are cylinders
with semispherical ends.
16. The method of claim 13, wherein the coldplate includes features
for mounting, aligning, and suspending the coldplate, and features
for accommodating cartridge heaters, thermocouples, and gas flow;
and wherein the coldplate and features are of unibody design.
17. The method of claim 13, further comprising side frames for
supporting a nest structure that includes the coldplate, wherein
the sideframes are pinned to a clamp plate such that the side
frames can be separated from the clamp plate and reassembled while
maintaining positional tolerances.
18. The method of claim 13, further comprising a pogo pin socket
having probe pins and supported by corner pins, the corner pins
supported by springs; wherein a load placed on the socket
compresses the corner pins and the probe pins of the socket.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field:
[0002] The present invention relates generally to integrated
circuit chip testing, and particularly to an improved functional
and stress testing apparatus.
[0003] 2. Description of Related Art:
[0004] High performance processor chips are frequently sorted by
various high performance metrics so they can be matched with the
class of machine for which they are intended. This typically
involves investigating chip performance using functional test
sequences at the extremes of various operational windows for
several variables, among these being chip voltage, clock speed,
power, and temperature. These test sequences at temperature
extremes can also identify early life failures and reduce the
likelihood of a faulty chip escaping and being assembled into
high-function and high-cost devices.
[0005] Processor chips are typically attached to a temporary
carrier (e.g., a temporary chip attach, or TCA) and then installed
in a device tester. The tester controls the applied voltage, the
clock frequency, the chip test sequences and power, and the chip
temperature. Tester architectures vary significantly, but primary
components typically include a test board that is compatible with
the class of device to be tested, a control computer to control the
test sequence, programmable power sources, other control hardware
to control delivery of test resources (voltage, current,
pneumatics, coolant fluid, etc.), a chiller to deliver a coolant
fluid to the device being tested, network interface and
communication hardware and software, and a test nest. The nest is
that portion of the tester that physically accommodates the device
under test (DUT).
[0006] Previous test apparatus suffered from shortcomings, such as
the inability to accurately and repeatedly register the coldplate
with respect to the TCA chip surface, which can contribute to chip
damage. Further, the external loads applied to the coldplate were
not well balanced, resulting in a poorly centered contact load
between the coldplate and chip surface, which detracts from the
thermal control performance of the assembly.
[0007] These and other issues are addressed by the present
invention.
SUMMARY OF THE INVENTION
[0008] The present invention teaches an innovative chip test system
and nest assembly. In a preferred embodiment, the nest assembly
provides an automated means of rapidly installing (and removing) a
TCA or other exposed chip Land Grid Array (LGA) devices onto a test
board site to facilitate high-volume testing. Preferred embodiments
of the present innovative nest assembly include a custom pogo pin
socket to electrically connect the TCA LGA substrate to the test
board by mechanically loading the TCA substrate into a test socket.
Preferred embodiments also include means to geometrically center
the load placed on the coldplate and chip for enhanced thermal
interface performance, and means to accurately position the contact
portion of the coldplate within the chip footprint while allowing
unrestrained planar alignment between the coldplate and chip
surfaces.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The novel features believed characteristic of the invention
are set forth in the appended claims. The invention itself,
however, as well as a preferred mode of use, further objectives and
advantages thereof, will best be understood by reference to the
following detailed description of an illustrative embodiment when
read in conjunction with the accompanying drawings, wherein:
[0010] FIG. 1 shows the innovative nest assembly consistent with a
preferred embodiment of the present invention.
[0011] FIG. 2 shows the innovative nest base assembly consistent
with a preferred embodiment of the present invention.
[0012] FIG. 3 shows the custom pogo pin socket consistent with a
preferred embodiment of the present invention.
[0013] FIG. 4 shows the actuator assembly to the nest base assembly
according to a preferred embodiment of the present invention.
[0014] FIG. 5 shows the actuator/coldplate assembly consistent with
a preferred embodiment of the present invention.
[0015] FIG. 6 shows the coldplate suspension according to a
preferred embodiment of the present invention.
[0016] FIG. 7 shows the coldplate assembly consistent with a
preferred embodiment of the present invention.
[0017] FIG. 8 shows a bottom view of the coldplate/load frame
consistent with a preferred embodiment of the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0018] FIG. 1 shows an innovative nest and test card assembly
consistent with a preferred embodiment. The nest is part of a chip
testing system and includes the region and apparatus where the DUT
is retained inside the testing system.
[0019] The primary components include air cylinder and coldplate
assembly 102 which is mounted directly to test card book assembly
112. Test card book assembly 112 is installed in a card cage where
it is connected to a tester backplane. The rear end of the card
cage contains bulkhead 110. Coolant line clamp 106 is mounted to
clamp support bracket 108, which is mounted to bulkhead 110.
Insulated coolant lines 104 supply chilled fluid to the nest region
(specifically the coldplate or heat sink) to control temperature of
the DUT.
[0020] The thermal performance of the system, i.e., uniformity of
cooling of the DUT by the coldplate, is sensitive to the net force
driving the DUT and coldplate together. The contact between the two
should be as uniform as possible, which means the forces acting on
the two should resolve at the vector center of the chip. Most of
the net force arises from the suspension springs (see below)
between the suspension mounting plate and the coldplate. However,
other forces (referred to herein also as parasitic forces) also
exist. For example, the wires that go to the heaters in the sink
act as springs, and when the sink moves, the wires bend, imparting
force. Also, coolant hoses 104 exert forces on the coldplate. The
force imbalance imparted by coolant hoses 104 can be mitigated in a
preferred embodiment using innovative adjustable clamp 106 that
allows the point where hoses 104 anchor to bracket 108 to be
changed. For example, the hoses can be allowed to hang free from
the bracket 108 so that they reach a zero force, or minimum energy
condition. The clamped end of the hose can then be moved using
clamp 108 so that in the minimum energy condition the other end of
the hose aligns to where it should be when attached to the
coldplate in the down position. In this way, the innovative clamp
allows for this particular parasitic force (i.e., that arising from
the hoses themselves) to be reduced or mitigated.
[0021] However, in a further innovation, the net force exerted by
the hoses on the coldplate and chip are not reduced to zero.
Instead, the clamp is used to manipulate the hoses into a position
where they balance and cancel other parasitic forces. For example,
if the net forces exerted on the coldplate by the wires (mentioned
above) is in one direction, a compensating force is introduced by
(for example) adjusting the clamp 106 holding hoses 104 to the
bracket 108. The system is adjusted in this way so that when the
nest is in the down position, the net forces exerted on the
coldplate are properly resolved and are geometrically centered
within the contact area between the coldplate and chip. By
balancing the forces on the coldplate in this way, the forces
between the coldplate and the chip surface are centered, improving
thermal performance of the interface.
[0022] Nest base assembly 200 is shown in FIG. 2. Base assembly 200
provides the means to register and retain pogo pin socket 204 and
provides the structural base to support and register the air
cylinder and coldplate assembly with respect to the DUT. Nest base
assembly 200 preferably includes pogo pin socket 204, although
other LGA socket technologies are applicable, which is clamped to
test board 206 between backside stiffener 218 and topside clamp
plate 202 using screws 216 that extend through stiffener 218,
insulator 210, card 206, socket 204 and engage threaded holes in
clamp plate 202. Backside stiffener 218 is preferably included to
limit deformation of board 206 and socket 204 under the high load
required to actuate socket 204 and electrically connect the DUT and
the test board 206. A G10 insulator 210 or similar material is
preferably used to insulate pads and other electrically conductive
features on test board 206 from backside stiffener 218, which is
preferably metallic. Backside stiffener 218 also preferably
includes a pair of cartridge heaters 212 which are controlled by
the test control code and are used to retard backside condensation.
Heaters 212 are held in place by heater retainers 214. One
advantage of clamping socket 204 to card 206 between two semi-rigid
structures (i.e., backside stiffener 218 and topside clamp plate
202) is the reduction of the effect of moisture absorption in the
socket body plastic, which can distort some critical dimensions in
the socket 204.
[0023] Nest site 208 shows where air cylinder and coldplate
assembly 102 is preferably positioned.
[0024] FIG. 3 shows custom pogo pin socket 300. The socket body is
preferably machined Torlon.TM. and contains an array 308 of 1657
pogo pin test probes, retained in the body by a backside retainer
plate in a preferred embodiment. Socket registration pins protrude
from both the top and bottom of the socket, and use spring loaded
corner support posts to support the DUT before engagement to the
pogo pins. (Note that in FIG. 3, only the corners of array 308 are
shown.) Clearance holes 310 are shown for mounting the socket 300,
as described previously. Socket 300 is registered to the LGA pad
array on the test board by two locator pins 302 that engage
alignment holes in the test card. Locator pins 302 protrude through
both sides of the socket body, providing registration of not only
the socket to the board, but of the topside clamp plate to the
socket and board. In preferred embodiments, the topside clamp plate
has alignment holes that engage alignment pins 302 on the socket
body. The DUT pocket 306 in the socket body is sized to accommodate
the tolerance range of the 42.5 mm nominal TCA device without
module centering devices. Additionally, the use of single-point
probes in the LGA connector mitigates the possibility of test
shorts or opens. Most pogo pin sockets used in LGA test
applications include a stripper plate, which is a spring loaded
plate that nominally rests above the exposed tip of the probe prior
to DUT installation, and hence affords a level of probe protection.
However, use of a stripper plate requires longer pogo pins, which
can degrade high frequency electrical performance. In the present
invention, it is preferred that no stripper plate is used. Instead,
four small spring-loaded corner pins 304 are used to support the
DUT above the exposed probe tips prior to pogo pin LGA socket
compression. These corner support pins 304 provide pogo pin
protection without compromising electrical performance.
[0025] FIG. 4 shows actuator assembly 402 and base or test board
book assembly 404. Actuator assembly 402 is preferably attached
directly to base assembly 404 via two side frames 406 that support
the structure. Side frames 406 are pinned to clamp plate 202 (see
FIG. 2), which allows teardown and reassembly of the structure for
maintenance or repair without disrupting the registration between
the actuator assembly and the socket. Additionally, module
protector 408 preferably is G10 material and is installed between
side frames 406 and the top clamp. This material protects the
exposed BSM (Bottom Surface Metallurgy) of the DUT as it is
installed in or removed from test socket 410. The top plate also
provides registration holes that accommodate a vacuum
pick/place/remove tool that picks up a DUT from a pickup station
with identical registration holes, and minimizes handling damage to
the DUT. This feature is feasible because the clamp plate is
accurately registered to the socket position via locator pins 302
in the socket body (see FIG. 3). Nest mounting assembly 412 is
mounted at nest site 208.
[0026] FIG. 5 shows an exploded view of the actuator/coldplate
assembly. The purpose here is to apply a load directly on the
perimeter of the TCA substrate, sufficient to create an electrical
interconnection between the TCA and the test board via the pogo pin
socket. For example, some applications require loads of about
150-160 lbs., depending on implementation. A second purpose of the
actuator/coldplate assembly is to position the coldplate onto the
exposed TCA chip surface, to allow the contact surfaces to align,
and to apply a load sufficient to create a good thermal interface.
An example implementation chip load is about 20-22 lbs., though
this value too can vary. Additionally, the coldplate/chip contact
load must be well controlled geometrically. If the contact load is
not driven sufficiently close to the geometric center of the chip,
the thermal interface performance is degraded.
[0027] The actuator/coldplate assembly includes a single-ended air
cylinder 502 mounted to the cylinder mounting plate 504, which
mounts directly to the side frames 406. A nest strain relief
bracket 506 is also retained by the cylinder attachment screws 508.
This bracket 506 is attached to the card cage chassis, which lends
sufficient stability to the entire nest structure to survive
typical shipping environments. A suspension mounting plate 510 is
attached directly to the working end of the air cylinder 502.
Suspension guide posts 512 are attached to the suspension mounting
plate 510 at the top, and to the load frame 514 at the bottom. The
suspension mounting plate/guide post/load frame assembly forms a
rigid structure, which applies load directly to the TCA substrate
perimeter when the air cylinder 502 is actuated. As the cylinder
502 is actuated the load frame 514 lowers until it engages the TCA
substrate, and a load develops between the load frame and the TCA
substrate. This load forces the TCA to the bottom of the socket
pocket, compressing the pogo pin probes and providing electrical
connection between the BSM of the TCA and the test card. Rotation
about a vertical axis of the load frame 514 (and coldplate assembly
that is suspended on the suspension mounting plate 510) is
restricted by a guide pin 516 that is pressed into the cylinder
mounting plate 504. An elongated clearance hole in the suspension
mounting plate 510 freely travels along the guide pin 516 during
actuation and retraction.
[0028] The coldplate suspension assembly is shown in FIG. 6.
Suspension mounting plate 602 is connected to the coldplate
assembly 604 and load frame 606 by load posts with suspension
springs 608. The purpose of the coldplate suspension is to allow
the coldplate pedestal 610 surface to align to the exposed chip
surface, and to develop a controlled contact load, geometrically
centered, between the coldplate and the chip. Additionally, the
coldplate pedestal must be accurately positioned within the
footprint of the chip. Pedestal overhang on a chip corner or edge
can create significant stress risers that can fracture the chip.
Hence, the pedestal is designed nominally smaller than the chip
footprint. Additionally, a radius is maintained on the pedestal
edge so that the contact stresses between the pedestal and chip are
mitigated as the coldplate aligns with the chip surface. For
example, the edges of pedestal 610 are rounded so that no sharp
edge touches the chip surface. Likewise, the corners of pedestal
610 are also rounded. This prevents the initial contact between
chip surface and pedestal 610 from involving a sharp corner or edge
against the surface of the chip.
[0029] The coldplate location with respect to the socket is
initially adjusted using a precision jig. This jig is temporarily
installed during nest assembly and precisely fits within the socket
pocket, and provides a cavity that precisely accommodates the
coldplate pedestal. The cylinder mounting plate is adjusted
laterally on the side frames until the coldplate pedestal is
properly registered within the precision jig cavity. Once it is
positioned, the top side frame screws are tightened, the precision
jig is removed, and no further adjustment is required. The nest can
be broken apart at the bottom of the side frames for repair or
maintenance and subsequently reassembled without disturbing the
registration of the coldplate with respect to the socket because
the side frames are pinned to the top clamp plate.
[0030] Coldplate assembly 604 includes tooling ball locator 612 as
described further below.
[0031] FIGS. 7 and 8 show the coldplate assembly 700. In a
preferred embodiment, the coldplate is a single integrated part.
All of the features required to mount, align, and suspend the
coldplate, as well as the features to accommodate cartridge heaters
(holes 704), thermocouples (thermocouple receptacle 706), and
helium flow (delivery port 708), are preferably integrated into a
single part. This unibody construction reduces coolant leaks and
makes the coldplate assembly more reliable. Cross flow channels are
machined into the one-piece coldplate body 710 to accommodate
coolant flow. End caps 712 are soldered directly onto the one-piece
body for reliability, and provide the inlet and outlet fittings 702
for the coolant hoses.
[0032] The coldplate is preferably free to move axially along the
load posts but compression springs maintain a preload which keeps
the coldplate biased against the load frame 606 in the unactuated
position. As the air cylinder is actuated, the suspension mounting
plate 602 and coldplate are driven toward the socket and DUT. The
coldplate pedestal 714 is preferably on the same plane as the
bottom of the load frame 606, so therefore as the coldplate
assembly approaches the DUT, initial contact will occur between the
coldplate pedestal and the chip surface. The air cylinder and
suspension mounting plate will continue downward until the load
frame contacts the perimeter of the TCA substrate, and then will
drive the TCA to the bottom of the socket pocket. As the load frame
engages the substrate, the coldplate separates slightly from the
load frame, a distance equivalent to the height of the chip with
respect to the TCA substrate (e.g., less than 1 mm). There is a
slight clearance between the load post clearance holes 720 and the
suspension guide posts 512, sufficient to allow the coldplate
suspension to rotate along the two orthogonal axes normal to the
verticle axis. Hence, the coldplate is free to tilt around either
the x- or y-axis in order to match the plane of the chip surface.
Once the coldplate separates from the load frame, these two
rotational degrees of freedom allow the coldplate pedestal to
freely align to the chip surface. As the coldplate aligns to the
chip surface, the transverse registration of the coldplate with
respect to the load frame (and hence with respect to the socket and
DUT) is maintained by a unique tooling ball locator feature 716.
The tooling balls are preferably precision steel spherical bodies
that are press fitted into the load flanges 718 of the coldplate
assembly (a.k.a. heatsink). In other embodiments, the tooling balls
are not spherical, but are actually cylindrical with rounded,
semi-spherical ends. These tooling balls engage precision cutouts
802 in the load frame (see FIG. 8, below). As the coldplate rotates
in the two available rotational degrees of freedom, the tooling
balls remain captured in the load frame retention feature, and
hence the transverse or XY positional registration of the coldplate
is maintained even as it rotates to align with the DUT chip surface
because the tooling balls prevent rotation about the z-axis
(vertical axis of the nest assembly) and restricts any transverse
motion of the coldplate with respect to the load frame.
[0033] The thermal performance of the coldplate/chip interface is
preferably enhanced by controlling the suspension forces and
external forces acting on the coldplate so that the resultant
contact force between the two is close to the geometric center of
the interface surfaces. As the contact force deviates from true
center, the contact pressure distribution between the two
components will become more variable, and the thermal interface
performance will degrade. Contact force centroid control is
achieved in a preferred embodiment primarily by using a low pivot
point on the heatsink, by using low stiffness compression springs
in the suspension, and by making the nominal preload compression of
the springs large with respect to the deviations that would occur
due to coldplate rotation during coldplate/chip surface alignment.
Additionally, the external loads acting on the coldplate, primarily
those from the coolant hoses, are preferably geometrically
symmetric which contributes to good contact force centroid
control.
[0034] To further enhance the contact load centroid control, an
adjustable coolant hose clamp bracket as shown in FIG. 1 is
included in preferred embodiments (as described above). Since the
major source of external loads acting on the coldplate come from
the coolant lines, a thermally insulated clamp made preferably from
a low thermal conductivity plastic (to retard condensation) is
provided that mounts directly to the bulkhead 110 of the test card
cage chassis. These clamps 106 preferably attach directly to the
coolant lines 104 (not the insulation) and can be adjusted on the
mounting bracket. As the mounting bracket is moved laterally, the
net contact force centroid location between the coldplate and the
chip surface can be adjusted. Once a position close to the
geometric center is achieved, the bracket is tightened and the
thermal performance is optimized. The hose clamps provide a stable
boundary condition for the coolant hoses, resulting in more
consistent contact load centroid performance over time.
Additionally, the coolant hose material is preferably selected to
provide the least stiffness change over the operating temperature
of the test nest, which also contributes to improved stability in
the contact load centroid performance.
[0035] The current innovations provide many advantages over prior
art systems. The primary advantages of the innovative nest design
include: accurate registration of gimbaled coldplate pedestal with
respect to the DUT using the tooling balls and engagement feature
on the load frame; balancing and control of external loads to
enhance load centroid thermal performance; integrated cold plate is
simpler and more reliable; pinned design allows easy teardown and
reassembly while maintaining positional tolerances (note that the
coldplate suspension registration adjustment is made at the top
plate on the side frames; once this adjustment is complete, the
nest can be broken at the bottom of the frames (which are precision
pinned) and hence reassembled without loss of registration);
concurrent registration of the card, socket, and topside clamp
plate using a single set of locator pins in the socket body; high
performance pogo pin socket design features enhance durability;
fixed socket pocket for easy installation/removal of DUT; clamped
socket mitigates dimensional sensitivity to moisture absorption;
single-point probes to accommodate DUT size tolerances without DUT
centering apparatus; simplified socket design eliminates stripper
plate and allows use of corner support posts for pogo pin
protection; mechanical integration of cooling apparatus and pogo
pin socket actuation; self-aligning coldplate to compensate for
planar misalignment between the test chip surface and the
coldplate; large throat to provide accessibility for DUT
installation/removal, eliminates need for complex clamshell
designs; coldplate suspension optimized for load centroid
performance (low pivot, soft springs, preload displacement with
respect to tolerances); mitigation of contact stress on chip via
radiused coldplate pedestal and registration control; load frame
with heatsink suspension provides independent loading of chip and
substrate.
[0036] The description of the present invention has been presented
for purposes of illustration and description, and is not intended
to be exhaustive or limited to the invention in the form disclosed.
Many modifications and variations will be apparent to those of
ordinary skill in the art. The embodiment was chosen and described
in order to best explain the principles of the invention, the
practical application, and to enable others of ordinary skill in
the art to understand the invention for various embodiments with
various modifications as are suited to the particular use
contemplated.
* * * * *